In numerous fields of technology it is required to apply very thin layers of pure substances on particular objects. Examples of this are window panes which are provided with a thin metal or metal oxide layer to filter out particular wavelength ranges from the sunlight. In the semiconductor technology often thin layers of a second substrate are applied onto a first substrate. Herein is of particular importance that the thin layers are not only very pure but must also be apportioned very precisely so that the particular layer thicknesses are exactly reproducible in each instance.
Thin layers can be applied by chemical or electrochemical deposition, by vapor deposition in a vacuum or by "sputtering" or cathode disintegration. In cathode sputtering there are provided in a vacuum chamber a gas discharge plasma, substance on a cathode to be sputtered--also called target--and a substrate to be coated.
An arrangement for applying thin layers on a substrate by means of the cathode sputtering method is already known in which between a cathode to be sputtered and an anode a mechanical shutter is provided which divides the space between the cathode and the substrate to be coated (EP-A-0 205 028). In this arrangement, however, only a relatively small fraction of the particles sputtered off the target deposits on the substrate.
Arrangements are known which function for the generation of charged particles which in turn can be used for a coating process (D. M. Goebel, G. Campbell and R. W. Conn in Journal of Nuclear Material 121, 1984, pages 277 to 282, North Holland Physics Publishing Division, Amsterdam; German Patent Application 38 03 355.0; German Patent Application P 38 34 984.1).
The present invention is based on the task of using particle sources in advantageous manner for the coating of substrates.
This task is solved according to the features of the present invention.
The advantage achieved with the invention comprises in particular in that nearly all chemical compounds, for example oxides, nitrides, etc. can be generated through DC current sputtering with very high deposition rates. In contract to conventional reactive sputtering in reactive atmospheres, in the invention ions of the reaction gas component are led directly from one or several sources disposed outside the sputter plasma to the substrate where they react with the atoms of the solid component sputtered off the target. Since these ions on the one hand are themselves very reactive and on the other hand upon their impinging on the substrate surface activate the latter, molecules, atoms and ions of the reactive gases can be largely kept away from the sputter target so that it can be sputtered in the metallic state.